Method for soil stabilization, more specifically, for stabilizing soil excavated from a trench using a calcium-magnesium composition

Abstract

The present invention relates to a method for stabilizing soil, the method comprising the steps of excavating and collecting material, providing a calcium magnesium compound, mixing the excavated material with the calcium magnesium compound to form a treated material, backfilling, and compacting to form a soil having an immediate support index of 5% or greater, wherein the step of providing a calcium magnesium compound comprises providing a calcium magnesium compound and an organic additive, and the method further comprises the steps of compacting the treated material and hardening the treated material to form a stabilized soil having a compressive strength Rc of 2 MPa or less after 28 days.

Description

[Technical field]

[0001] This invention relates generally to a method of improving soil known as soil stabilization, and more particularly to soil excavated from trenches, and to calcium-magnesium compositions that can be used for this purpose.

[0002] More particularly, a method for stabilizing soil, and more particularly soil excavated from a trench, includes the steps of: a) excavating material to form one or more trenches and collecting the excavated material having a predetermined moisture content; b) providing the excavated material with a calcium-magnesium compound; c) mixing the excavated material with a calcium-magnesium compound to form a treated material having a moisture content lower than that of the excavated material; d) backfilling the trench with treatment material after placing the buried elements; e) compacting the treated material placed in the backfill; f) A process for forming soil with an immediate support index of 5% or more. [Background technology]

[0003] Soil treatment with calcium-magnesium compounds is a technique widely used in civil engineering to make unsuitable soils (usually fine clayey sands or silty clay soils) usable for construction, especially backfilling.

[0004] Calcium-magnesium compounds help dry the soil and improve its compressibility, thus providing the desired bearing capacity.

[0005] Soil treatment with lime or other calcium-magnesium compounds has short-, medium- and long-term effects. In the short term, soil improvement results in drying, flocculation of clay particles, better compaction properties and improved bearing capacity. In the medium to long term, however, stabilized soils experience a significant increase in the strength of the soil-forming material due to the pozzolanic reaction between the clay minerals, especially the aluminium silicate components, and the added lime.

[0006] Soil treatment techniques are used to facilitate the direct reuse of excavated soils, especially clayey silts and plastic soils with high water content, instead of being disposed of and stored in landfill sites, and dry sand and soil are transported to the site for backfilling. This technology brings a circular economy to the civil engineering industry.

[0007] In applications where re-excavation of treated soils is required after several months to years, a drawback of current technology is that the strength of the soil-forming material increases excessively, making excavation impossible by hand or with lightly equipped equipment.

[0008] In trench construction, the excavated soils are generally wet or saturated with water. These soils are treated with lime to dry, aggregate and make them directly reusable in trench backfill. When using freshly excavated soils, large amounts of lime are used to accelerate the drying of the soil, making the treated soil directly reusable, but the large amounts of lime required for drying subsequently lead to hardening between the lime and the clay minerals, resulting in a material that is too hard. The lime-treated soils end up with fundamentally different properties from the surrounding soils and the original soil. This results in problems during re-excavation, risks of cracked pipes and failure of material interfaces.

[0009] No. 5,716,448 describes a method for converting excavated soil into a liquid backfill or mortar by adding a hydraulic solidifier (cement or hydraulic lime) and a flow agent (water) plus additives to the excavated soil. The document describes the addition of sugars and cement dispersants as additives.

[0010] Hydraulic binders, known to those skilled in the art, harden by themselves in the presence of water: the calcium silicate of the hydraulic binder reacts with water to form a calcium silicate hydrate (CSH) phase.

[0011] According to the document, the resulting mortar must maintain adequate fluidity for a significant period of time (up to 90 minutes) to facilitate application, exhibit good minimum ultimate strength (measured after 7 and 28 days), and exhibit little or no drying cracking.

[0012] A detailed analysis of this document reveals that when cement is used as hydraulic binder and starch syrup is added at 1.5% by weight, the compressive strengths measured at 7 and 28 days are 3.04 MPa and 8.43 MPa, respectively. Similar results are obtained with glucose. Lime is mentioned as a hydraulic material, but the document does not show any examples of its use as a hydraulic binder.

[0013] JP 59-84972 describes the use of a soil stabilizing composition that delays initial hardening and setting, allows hardening and setting during pouring, and rapidly reaches the desired minimum compressive strength at a subsequent stage.

[0014] The soil stabilization composition contains 0.1 to 10 parts by weight of a sugar based on 100 parts by weight of a cement / lime component obtained by mixing cement and lime in a weight ratio of 99:1 to 70:30.

[0015] The sugar may be sucrose, glucose, fructose, galactose, maltose, blackstrap molasses, brown sugar, etc. Hydroxycarboxylic acid may be added. In this case, the amount of sugar and oxycarboxylic acid is limited to the range of 0.1 to 10 parts by weight per 100 parts by weight of cement-lime compound. On the other hand, the content of sugar relative to the weight of lime is 5 to 60% by weight.

[0016] According to the document, the lime content must be limited, otherwise the compressive strength of subsequent stages (measured at 28 days) will be insufficient.

[0017] As can be seen, the work carried out in accordance with these prior documents has focused on delaying hardening and initial set to maintain short-term workability and minimize subsequent hardening in order to improve handling when placing treated soils, without being concerned with controlling hardening and compressive strength in subsequent stages. Summary of the Invention [Problem to be solved by the invention]

[0018] The present invention aims to overcome the drawbacks of the prior art by providing a method for stabilizing soils, more specifically soils excavated from trenches, ensuring a short-term improvement in a few hours (immediate and sufficient bearing capacity due to reduction in moisture content and cohesion) equivalent to that achieved by using standard quicklime (of the air type as defined in standard EN459-1, section 4.3.1) and moderately increasing the strength of the material in the medium to long term, while controlling the reaction of calcium-magnesium compounds (lime) with clay minerals.

[0019] The present invention aims to control the set and compressive strength to a maximum value over an extended period of time (months or years), and is therefore in opposition to the prior art mentioned above, which aims for a long-term minimum value in a shorter period of time. [Means for solving the problem]

[0020] In order to solve this problem, the present invention provides a method as indicated at the beginning, characterized in that the supply of the calcium-magnesium compound is in the form of a calcium-magnesium composition, in which the calcium-magnesium compound and an organic additive are supplied together or separately, the organic additive being selected, for example, from monosaccharides, disaccharides, oligosaccharides, polysaccharides and derivatives thereof, more particularly from galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed products, more particularly from galactose, mannose, xylose, glucose, fructose , saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, invert sugar syrup, arabinose, ribose, maltose, lactose, cellulose, modified cellulose, maltotriose, raffinose, sugar alcohols, such as sorbitol, glucitol, erythritol, lactitol, maltitol or xylitol, carboxylic acids and their salts, more particularly uronic or aldonic acids, such as gluconic acid or sodium gluconate, inulin or modified inulin, pectin, dextrins and cyclodextrins, and mixtures thereof. The method further comprises the step of hardening the treated and compressed material and, after the step of compressing the treated material, further comprises the step of compressing the treated material to form a stabilized soil having a compressive strength Rc of 2 MPa or less, preferably 1.5 MPa or less, more preferably 0.7 MPa or less, more preferably 0.1 MPa or more, preferably 0.2 MPa or more, after 28 days, advantageously at 40°C.

[0021] Thus, the method according to the invention allows the stabilized soil to have a compressive strength Rc of not more than 2 MPa after 28 days at 40°C, thereby allowing the hardening at a subsequent stage to be controlled, whereas standard liming treatment produces a compressive strength Rc of 3 MPa or more after 28 days at 40°C, without compromising the immediate bearing capacity.

[0022] The method according to the invention therefore makes it possible to treat excavated soil without using other soil as raw material. Moreover, if the stabilized soil obtained using the method according to the invention needs to be excavated again, it can be easily recovered and, optionally, treated again according to the method according to the invention, depending on the user's requirements.

[0023] The compressive strength is measured by simulating the process in a laboratory at Proctor Optimum.

[0024] The Proctor Optimum is determined by the standard Proctor test described in the standard EN13286-2 ("Unconsolidated and hydraulic mixes - Part 2: Test methods for reference density and moisture content in the laboratory - Proctor compaction"). The Proctor Optimum refers to the moisture content at which the maximum dry density is obtained by compaction, which corresponds to the maximum compaction state and maximum strength capacity at a defined energy. In the context of the present invention, test samples were prepared in a CBR formwork 152 mm high and 152 mm in diameter (according to the NF P 94 093 standard) by compacting soil samples treated according to the present invention, treated with lime or untreated soil samples.

[0025] The Immediate Support Index (IBI) measures the deformation resistance of the soil under investigation. In particular, it characterizes the soil's ability to allow machine movements on the site. It is expressed as a percentage of the stress that develops in a reference material while applying a given compression to the soil under investigation. By definition, this index corresponds to the greater of the two values ​​obtained by applying the following formula according to the EN 13286-47 standard: JPEG2025511265000001.jpg29106

[0026] Furthermore, the cylindrical punch that applies the force should preferably have a diameter of (50±0.5) mm (EN 13286-47).

[0027] Test specimens are prepared in a California bearing ratio mold using a conventional Proctor consolidation test and placed in an IBI press system with a compression speed of 1.27 mm / min. A pressure curve is obtained based on the compression. The curves are optionally correlated and the maximum of the values ​​IBI25 and IBI50 is calculated as the IBI. This test is described in the standard EN 13286-47 ("Unbound and hydraulic mixes - Part 47: California shear test, method for determination of instantaneous bearing index and linear expansion").

[0028] The simple compression test is carried out according to the standard NF EN 13286-41. An axial force is applied to the specimen and maintained until fracture. The simple compressive strength Rc is defined as the stress measured at fracture. The equipment used for this test is a press that meets the criteria of the standard EN 13286-41.

[0029] A test specimen of natural or treated soil is placed between two parallel plates of a press. The axis of the specimen is perpendicular to the plates. The load application complies with the aforementioned standard EN 13286-41. The maximum load received by the specimen is recorded. The simple compressive strength is calculated according to the following formula: Rc=F / Ac Where: Rc(N / mm 2 or MPa): Simple compressive strength F(N): Maximum load applied to the test specimen Ac(mm 2 ): Cross-sectional area of ​​the test piece

[0030] Simple compression tests are performed on at least two specimens. The simple compressive strength of the sample is the arithmetic mean of the values ​​obtained.

[0031] The 28-day compression test is carried out by maintaining the specimens under well-defined temperature conditions of 20° C. or 40° C. The 40° C. temperature is preferred as the results obtained reflect longer-term performance and allow for the simulation of long-term curing (more than 1 year).

[0032] During the 28-day curing period, the test specimens are sealed in plastic film and plastic bags to keep their moisture content constant. The specimens are stored in a thermostatic chamber at 40°C. The test specimens are removed from the bags and plastic film immediately before the simple compression test.

[0033] Moreover, according to the invention, the soil treatment process does not require special equipment or other practical modifications, and the calcium-magnesium compounds and organic additives are supplied in doses equivalent to those of standard quicklime, so that they do not interfere with application methods at construction sites. However, the method according to the invention makes it easier to re-excavate the soil-forming material, which can be done manually or with light equipment if necessary, limiting the risk of damage to surrounding elements such as pipes and cables in the application of the trench, and also preventing cracks in the road covering the newly filled trench.

[0034] In a particular embodiment of the invention, the calcium-magnesium compound of the calcium-magnesium composition is quicklime or a quick compound having an effective CaO content of at least 40% by weight, preferably at least 50% by weight, more particularly at least 65% by weight, preferably at least 70% by weight, more preferably still at least 75% by weight, advantageously at least 80% by weight and more advantageously still at least 90% by weight, relative to the calcium-magnesium compound.

[0035] The effective CaO content is advantageously determined according to standard EN 459-2.

[0036] Preferably, the skilled person is aware of different classes of quicklime, such as classes CL70, CL80, CL90, in particular those contained in standard EN 459-2, which may contain an effective CaO content of 55 or more, 65 or more, 80 or more, respectively. These types of quicklime are also part of the present invention and can be combined with the embodiments described throughout this specification.

[0037] According to a preferred embodiment, the calcium-magnesium compound is quicklime, in particular air lime, having at least one of the following properties: - Total CaO and MgO content is 70% or more by weight, and effective CaO content is 55% or more by weight - Total CaO and MgO content is 80% or more by weight, and effective CaO content is 65% or more by weight - Total CaO and MgO content is 90% or more by weight, and the effective CaO content is 80% or more by weight Quicklime is divided into two subspecies: calcium lime (CL) and dolomitic lime (DL).

[0038] According to an advantageous embodiment, the calcium-magnesium compound is quicklime, in particular air lime, having at least one of the following characteristics: a total CaO and MgO content of at least 70% by weight, in particular at least 80%, preferably at least 88%, for example at least 90% by weight, in particular at least 95% by weight, and / or an effective lime content of at least 50% by weight, more particularly at least 55% by weight, preferably at least 55% by weight, more preferably still at least 70% by weight, preferably at least 85% by weight, advantageously at least 90% by weight, more advantageously still at least 93% by weight.

[0039] According to a particularly advantageous embodiment, the calcium-magnesium compound has a particle size d 99 is less than 2 mm, and the particle diameter d 50 is greater than 3 μm, more particularly greater than 4 μm and less than or equal to 90 μm.

[0040] In the context of the present invention, the calcium-magnesium compound is preferably quicklime, in particular air quicklime. Air lime is divided into two subspecies: calcium lime (CL) and dolomitic lime (DL). This embodiment makes it possible to further improve the results obtained. The combination of quicklime and organic additives according to the invention is advantageous in that it makes it possible to obtain surprising results.

[0041] Quicklime is understood to mean a solid mineral whose chemical composition is mainly calcium oxide, CaO. Quicklime is generally obtained by calcining limestone, which consists mainly of calcium oxide, CaCO3. Quicklime contains up to a few percent of impurities, namely compounds of magnesium oxide, MgO, silica, SiO2 or alumina, Al2O3. These impurities are expressed in the above forms, but in practice may appear in different phases. It also contains a few percent of residual calcium carbonate (CaCO3), commonly called unburned.

[0042] Moreover, the skilled person is aware of dolomitic lime with a magnesium content of more than 5%, and this value can be even higher, depending on the type of dolomitic lime used: for example, lime commonly referred to as DL85 can contain more than 30% MgO by weight relative to the weight of calcium-magnesium compounds, when measured according to the EN 459-1 standard.

[0043] The expression "excavated material" preferably refers to fine clayey sandy soil or silty clayey soil. This material has a certain moisture content depending on its nature, so that silt contains 15-25% moisture by weight or more, sand contains 3-10% moisture or more, clay contains 20-40% moisture or more. These contents are expressed based on the weight of the dry substance. It is clear that other types of soil can also be used and are known to the skilled person.

[0044] Advantageously, the soil in the context of the present invention has an organic matter content of up to 6% by weight, as defined in standard 16907-2:2018 or NBN EN 16907-2:2019. The present invention also preferably provides for the treatment of soils having an organic matter content of less than or equal to 2% by weight and / or soils that are substantially free of organic matter, i.e. of the order of 0.1% by weight, preferably 0% by weight. The organic matter content in soils according to the present invention can thus be between 0 and 6% by weight.

[0045] Thus, by adding the calcium-magnesium compound and organic additives according to the present invention to the excavated material, it is possible to reduce the moisture content of the treated material (i.e., dry the treated material), so that the treated material contains less moisture than the starting material.

[0046] The method according to the invention includes a step of backfilling the trench with a treatment material after placing the elements to be buried, which may be any construction material present underground, such as ducts (water, gas, etc.), pipes, electricity lines, accessories, sewers, etc.

[0047] It should be noted that advantageously, soils formed within the scope of the present invention have an immediate support index of 5% or more, preferably 7% or more, and more preferably 10% or more.

[0048] In practical cases known to those skilled in the art, the support index can also be 12% or more, 15% or more, 20% or more, 25% or more, 30% or more. The immediate support index can also exceed a value of 30%.

[0049] It should be noted that the aforementioned bearing index values ​​can be combined with each other.

[0050] Advantageously, in the method according to the invention, the calcium-magnesium compound is provided in a ratio by weight of calcium-magnesium compound to the weight of excavated dry material of 1 to 10% by weight, in particular 1 to 5% by weight, more particularly 1 to 3% by weight.

[0051] In a particular embodiment of the method according to the invention, the additive is provided in a proportion of 2 to 10% by weight of the organic additive, preferably 3 to 7% by weight of the organic additive, more particularly 4 to 6% by weight of the organic additive, or in a proportion of more than 10% to 20% by weight of the organic additive, relative to the weight of the calcium-magnesium compound.

[0052] Particularly advantageously, according to the invention, the organic additive is selected from sugars and their derivatives, such as, for example, monosaccharides, disaccharides, oligosaccharides, polysaccharides and their derivatives, more particularly from galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, invert sugar syrup, arabinose, ribose, maltose, lactose, cellulose, modified cellulose, maltotriose and raffinose, sugar alcohols, such as, for example, sorbitol, glucitol, erythritol, lactitol, maltitol or xylitol, carboxylic acids and their salts, in particular uronic or aldonic acids, such as gluconic acid or sodium gluconate, inulin or modified inulin, pectin, dextrin, cyclodextrin and mixtures thereof.

[0053] According to a preferred embodiment of the invention, the organic additive is, for example, selected from mono-, di-, oligo- and polysaccharides and their derivatives, more particularly from galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, invert sugar syrup, arabinose, ribose, maltose, lactose, cellulose, modified cellulose, maltotriose and raffinose, sugar alcohols, such as sorbitol, glucitol, erythritol, lactitol, maltitol or xylitol, and mixtures thereof.

[0054] More particularly, according to the invention, the calcium-magnesium compound is quicklime, in particular air quicklime, which is divided into two subspecies: calcium lime (CL) and dolomitic lime (DL).

[0055] Preferably, air lime is more precisely defined in standard EN-459-1 for building lime.

[0056] According to this standard, the term "lime" refers to both calcium lime and dolomitic lime, and to calcium oxide and / or hydroxide, calcium magnesium oxide and / or calcium hydroxide produced by the thermal decomposition (calcination) of natural calcium carbonate (limestone, chalk, shells, etc.) or natural calcium magnesium carbonate (dolomitic limestone, dolomite, etc.).

[0057] According to this standard, air lime is a type of lime mentioned above, which hardens by combining with carbon dioxide in the air. Air lime does not have hydraulic properties. Air lime is divided into two sub-types: calcium lime (CL) and dolomitic lime (DL).

[0058] Hydraulic lime, on the other hand, is a building lime composed primarily of calcium hydroxide, calcium silicate, and calcium aluminate. Hydraulic lime has the property of hardening when mixed with or in contact with water, or even in water. Reaction with atmospheric carbon dioxide is also part of the hardening process. Hydraulic lime is classified into three subfamilies: natural hydraulic lime (NHL), formulated lime (FL), and hydraulic lime (HL).

[0059] Hydraulic lime is a binder made of lime and other materials such as cement, blast furnace slag, fly ash, or other suitable materials. Hydraulic coal has the property of hardening in water. Carbon dioxide from the atmosphere contributes to the hardening process.

[0060] Air lime can either (1) react with atmospheric CO2 and harden to CaCO3, or (2) harden via a pozzolanic reaction, which occurs when the ash or clay of pozzolanic materials containing silica and alumina are activated or solubilized, respectively, by the high pH generated by lime in the soil and react with calcium in the air to form calcium silicate.

[0061] Further embodiments of the method according to the invention are set forth in the accompanying claims.

[0062] The present invention also relates to a powder composition comprising a calcium-magnesium compound and an organic additive, characterized in that the organic additive is present in the powder composition in an amount sufficient to form a stabilized soil, more particularly an excavated soil, which has an immediate support index of 5% or more and a compressive strength Rc of 2 MPa or less after 28 days, preferably at 40°C.

[0063] Thus, preferably, the powder composition consisting of the calcium-magnesium compound and the organic additive can be mixed with a material, preferably an excavated material such as soil, preferably a moist soil, in particular a silty soil or a clay soil or a sandy clay soil.

[0064] In certain embodiments, the composition has a t of 20 minutes or more, particularly 30 minutes or more, particularly 60 minutes or more, more particularly 80 minutes or more, and even more particularly 100 minutes or more. 60 Advantageously, the composition has a t of less than 150 minutes. 60 All the above values ​​can be combined with each other.

[0065] Advantageously, the calcium-magnesium compound is selected in a weight ratio of quicklime and at least 40% by weight, preferably at least 50% by weight, more particularly at least 65% by weight, preferably at least 70% by weight, even more preferably at least 75% by weight, advantageously at least 80% by weight and even more advantageously at least 90% by weight, relative to the weight of the calcium-magnesium compound.

[0066] According to a preferred embodiment, the calcium-magnesium compound is quicklime, in particular air lime, having at least one of the following properties: - Total CaO and MgO content is 70% or more by weight, and effective CaO content is 55% or more by weight - Total CaO and MgO content is 80% or more by weight, and effective CaO content is 65% or more by weight - Total CaO and MgO content is 90% or more by weight, and the effective CaO content is 80% or more by weight

[0067] According to an advantageous embodiment, the calcium-magnesium compound is quicklime, in particular air lime, having at least one of the following characteristics: a total CaO and MgO content of at least 70% by weight, in particular at least 80%, preferably at least 8%, for example at least 90% by weight, in particular at least 50%, more particularly at least 55%, preferably at least 55%, more preferably still at least 70%, preferably more than 85%, advantageously more than 90% and more advantageously still more than 93%.

[0068] Air lime is divided into two subspecies: calcium lime (CL) and dolomitic lime (DL).

[0069] According to a particularly advantageous embodiment, the calcium-magnesium compound has a particle size d 99 is less than 2 mm, and the particle diameter d 50 is greater than 3 μm, more particularly greater than 4 μm and up to 90 μm.

[0070] Preferably, the organic additive is present in an amount of at least 2% by weight, preferably at least 3% by weight, more preferably at least 4% by weight, more preferably at most 10% by weight, preferably at most 7% by weight, more preferably at most 6% by weight, or in an amount of 10-20% by weight, based on the weight of the calcium-magnesium compound.

[0071] The organic additives are, for example, selected from monosaccharides, disaccharides, oligosaccharides, polysaccharides and derivatives thereof, more particularly galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, invert sugar syrup, arabinose, ribose, maltose, lactose, cellulose, modified cellulose, maltotriose and raffinose, sugar alcohols, such as sorbitol, glucitol, erythritol, lactitol, maltitol or xylitol, carboxylic acids and their salts, in particular uronic or aldonic acids, such as gluconic acid or sodium gluconate, inulin or modified inulin, pectin, dextrin, cyclodextrin and mixtures thereof.

[0072] According to a preferred embodiment, the organic additive is, for example, selected from monosaccharides, disaccharides, oligosaccharides, polysaccharides and their derivatives, more particularly selected from galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, invert sugar syrup, arabinose, ribose, maltose, lactose, cellulose, modified cellulose, maltotriose and raffinose, sugar alcohols, such as sorbitol, glucitol, erythritol, lactitol, maltitol or xylitol, and mixtures thereof.

[0073] More preferably, the calcium-magnesium compound is quicklime having at least one of the following characteristics: a total available CaO and MgO content of at least 80% by weight and an available lime content of at least 70%.

[0074] According to a preferred embodiment, the calcium-magnesium compound is quicklime, in particular air quicklime, which is divided into two subspecies: calcium lime (CL) and dolomitic lime (DL).

[0075] Further embodiments of the powder composition according to the invention are indicated in the appended claims. It should be noted that all the features of the above-mentioned methods can be combined with the preferred embodiments described for the composition according to the invention.

[0076] The present invention also relates to a product for any use in the field of construction, civil engineering, earthworks or in the field of soil stabilization, in particular excavated soils, which product can be obtained by the method according to the invention, which product has a compressive strength Rc of less than or equal to 2 MPa after 28 days, preferably at 40°C.

[0077] All the features described above for the method and / or composition as described for the composition of the invention can also be combined with the preferred embodiments described for the product according to the invention.

[0078] Furthermore, the present specification also relates to the use of the powder composition according to the invention, preferably in the construction or civil engineering field, for treating excavated material to form a stabilized soil having an immediate support index of 5% or more and a compressive strength Rc of 2 MPa or less after 28 days, preferably at 40° C.

[0079] All the characteristics described above for the method and / or composition and / or product as described for the product of the invention can also be combined with the preferred embodiments described for the use of the powder composition according to the invention.

[0080] Further embodiments of the products and uses according to the invention are set forth in the accompanying claims.

[0081] The symbol dx stands for the diameter expressed in μm, measured by laser diffraction granulometry using methanol as carrier solvent, and means that X% by volume of the measured particles or grains are less than or equal to this diameter. Prior to the measurement, the sample is subjected to ultrasonic treatment for 120 seconds to improve the dispersion of the particles without the risk of breaking them.

[0082] The reactivity of quicklime is generally characterized and measured by the procedure disclosed in European Standard EN 459-2 (§6.6). It is also used to characterize the reactivity of quicklime by adding 150 g of quicklime to a volume of 600 cm3 of water initially at 20 °C. 3 The time it takes for the temperature to reach 60°C is t 60 It is quantified by:

[0083] Preferably, the calcium-magnesium compound of the calcium-magnesium composition is quicklime, in particular airlime, which is divided into two sub-types: calcium lime (CL) and dolomitic lime (DL). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0084] Further characteristics, details and advantages of the present invention are explained hereinafter in a non-limiting manner with reference to the drawings and examples.

[0085] The present invention relates to a method, composition, product and application of soil stabilization, preferably in the field of construction or civil engineering. The product in particular consists of a mixture of quicklime (optionally partially combined with a hydraulic binder) and organic additives. This mixture is, for example, mainly (50% to more than 90%) composed of standard quicklime (optionally partially combined with a calcium-based hydraulic binder) and contains 2% to 10%, more particularly 3% to 7%, in particular 4% to 6%, even more particularly 5%, or even 10% to 20% by weight of organic additives (optionally partially combined with a calcium-based hydraulic binder) relative to the standard quicklime.

[0086] The calcium-magnesium composition according to the invention is used for the treatment of particularly wet soils, especially silty, clayey and sandy clay soils, resulting in a reduction in water content, flocculation of clay minerals and an immediate bearing capacity equivalent to standard treatment with quicklime. In the medium to long term, the composition according to the invention controls the pozzolanic reaction and moderately increases the strength of the material. This property allows the treated material to be excavated manually or with light equipment after several months or years, facilitating the compressibility of the treated volume and similar behavior to the surrounding soil, as well as limited strength development.

[0087] The pozzolanic reaction is controlled by optimally adjusting the organic additives. (1) It maintains the drying effect associated with the exothermic reaction of quicklime to form calcium hydroxide. (2) Maintains the coagulation effect of calcium hydroxide on clay minerals. (3) Control the amount of available (free) lime. (a) increasing the pH to solubilize the silica and alumina in the clay and silt contained in the treated soil; (b) The pozzolanic reaction is carried out in a controlled manner to promote the development of strength and elastic modulus E.

[0088] The production process of calcium-magnesium compositions is preferably carried out using an industrial mixture of calcium-magnesium compounds, especially as quicklime, in the lime plant, in a mixing plant with organic additives or in a subsequent mixing operation. Likewise, a two-component supply at the construction site combining a mixed dose of calcium-magnesium compounds with organic additives can also be carried out.

[0089] In the examples referred to below, the following standards were used: the immediate bearing capacity index is measured according to standards EN 13286-47 and / or NF P 94-078, the compressive strength Rc can be measured according to standards EN 13286-41 and / or NF P94-077.

[0090] Example 1 Comparative Example 1 A silty soil (VBS = 2.59 g / 100 g) was treated with 2% standard quicklime (CL90, available CaO = 91.2%, t 60 = 5.2 min) is added.

[0091] The immediate bearing capacity index (IBI) at the water content corresponding to the Proctor optimum (wOPN = 16%) is 33%.

[0092] After hardening (storage in a closed environment), the compressive strength Rc measured at 40 °C for 28 days corresponds to 3.88 MPa (wOPN = 16%, dry density = 98.5% of OPN).

[0093] Example 1 according to the present invention The same soil is treated with 2% (relative to the soil dry mass) of a mixture according to the invention, made of 95% calcium-magnesium compounds (100% standard quicklime) and 5% sucrose. The instantaneous support index (IBI) during compaction at the Proctor optimum (wOPN=16%) is 32%.

[0094] The compressive strength (Rc) measured after 28 days of curing (storage in a closed environment) at 40°C corresponds to 1 MPa (wOPN = 16%, dry density = 95% OPN). Testing at 40°C is generally recognised as simulating long-term curing potential (several years).

[0095] It can be seen that the immediate bearing capacity index of Comparative Example 1 is similar to that of Example 1 according to the invention. However, with regard to the compressive strength Rc after 28 days at 40° C., Example 1 according to the invention is particularly advantageous, showing an Rc value of less than 2 MPa.

[0096] Example 2 Comparative Example 2 The same soil as in Example 1 is treated with the same quicklime as in Example 1 at a rate of 2% based on the dry mass of the soil.

[0097] The immediate support index (IBI) is 24% when the moisture content at compression is 20%.

[0098] The compressive strength measured after 28 days of curing at 40°C (storage in a closed environment) was 3.07 MPa (w=20%, dry density=98.5% OPN).

[0099] Example 2 according to the present invention The same soil is treated with a mixture according to the invention at a rate of 2% relative to the dry mass of the soil, which is made up of 95% calcium-magnesium compounds (100% standard quicklime) and 5% sucrose.

[0100] The immediate support index (IBI) at 20% moisture content during compression is 18%.

[0101] After hardening (storage in a closed environment), the compressive strength (Rc) measured at 40°C for 28 days corresponds to 1 MPa (w=20%, dry density=95% OPN). Testing at 40°C is generally recognized to simulate the potential for long-term hardening (several years).

[0102] It can be seen that the immediate bearing capacity index of Comparative Example 2 is similar to that shown in Example 2 according to the invention. However, with regard to the compressive strength Rc after 28 days at 40° C., Example 2 according to the invention shows an Rc value of less than 2 MPa, which is particularly advantageous.

[0103] Example 3 Comparative Example 3 A silty soil (VBS = 2.5 g / 100 g, percentage of particles passing at 80 μm = 97%) is treated by adding quicklime 0 / 90 μm (free CaO = 94.5%, t60 = 2.4 min) at a rate of 2% based on the dry mass of the soil.

[0104] The immediate support index (IBI) at a moisture content of 20% before treatment corresponds to 9%.

[0105] Under the same moisture content conditions, the compressive strength measured after 28 days of curing at 40°C (storage in a closed environment) corresponds to 2.92 MPa (dry density = 95% OPN).

[0106] Example 3 according to the present invention The same soil was mixed with 95% calcium-magnesium compounds (100% standard quicklime) and 5% sucrose at a ratio of 2.1% based on the soil's dry mass.

[0107] The immediate support index (IBI) at 20% moisture content before treatment is equal to 9%.

[0108] The compressive strength (Rc) measured after 28 days of curing at 40°C (storage in a closed environment) is equal to 1.69 MPa (dry density = 95% OPN).

[0109] It can be seen that the immediate bearing capacity index of Comparative Example 3 is similar to that of Example 3 according to the invention. However, with regard to the compressive strength Rc after 28 days at 40°C, Example 3 according to the invention shows an Rc value of less than 2 MPa, which is particularly advantageous.

[0110] It will be understood that the invention is not limited to the embodiments described above, but that many modifications can be made without departing from the scope of the appended claims.

Claims

1. 1. A method for stabilizing soil, particularly soil excavated from a trench, said method comprising the steps of: a) excavating material to form one or more trenches and collecting the excavated material having a predetermined moisture content; b) providing said drilled material with a calcium-magnesium compound; c) mixing the drilled material with the calcium-magnesium compound to form a treated material having a moisture content lower than that of the drilled material; d) backfilling said trench with said treatment material after placing the embedded element; e) compacting the treatment material disposed in the backfill; f) forming a soil having an immediate support index of 5% or greater. The calcium-magnesium compound supply is a supply in the form of a calcium-magnesium composition, in which the calcium-magnesium compound and the organic additive are supplied together or separately, the organic additive being selected from sugars and their derivatives, such as monosaccharides, disaccharides, oligosaccharides, polysaccharides and their derivatives, more particularly galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, invert sugar syrup, arabinose, ribose, maltose, lact ... cellulose, modified cellulose, maltotriose and raffinose, sugar alcohols such as sorbitol, glucitol, erythritol, lactitol, maltitol or xylitol, carboxylic acids and their salts, more particularly uronic or aldonic acids such as gluconic acid or sodium gluconate, inulin or modified inulin, pectin, dextrin, cyclodextrin and mixtures thereof, said method further comprising the step of hardening the treated and compacted material after the step of compressing the treated material to form a stabilized soil having a compressive strength Rc of 2 MPa or less after 28 days.

2. 2. A method for stabilising soil, in particular soil excavated from a trench, according to claim 1, wherein the calcium-magnesium compound of the calcium-magnesium composition is quicklime or a quick compound having an effective CaO content of at least 40% by weight, preferably at least 50% by weight, in particular at least 65% by weight, preferably at least 70% by weight, even more preferably at least 75% by weight, advantageously at least 80% by weight and even more advantageously at least 90% by weight, based on the weight of the calcium-magnesium compound.

3. 3. A method for stabilising soil, in particular soil excavated from a trench, according to claim 1 or 2, in which the supply of calcium-magnesium compounds is carried out at 1 to 10% by weight, more particularly 1.5 to 5% by weight, of said calcium-magnesium compounds, relative to the weight of the excavated dry material.

4. 4. A method for stabilising soils, in particular soils excavated from trenches, according to any one of claims 1 to 3, in which the additive is added in a proportion of 2 to 10%, preferably 3 to 7%, more particularly 4 to 6% by weight of the organic additive relative to the weight of the calcium-magnesium compound, or in an amount of more than 10% and less than 20% by weight of the organic additive.

5. 5. A method for stabilising soil, in particular soil excavated from a trench according to any one of claims 1 to 4, wherein the calcium-magnesium compound is lime, in particular quicklime.

6. A powder composition comprising a calcium magnesium compound and an organic additive, The organic additive is present in the powder composition in an amount sufficient to form a stabilized soil, in particular an excavated soil, having an immediate support index of at least 5% and a compressive strength Rc of at most 2 MPa after 28 days, preferably at 40° C., the organic additive being, for example, selected from monosaccharides, disaccharides, oligosaccharides, polysaccharides and derivatives thereof, more particularly galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, invert 1. A powder composition selected from sugar syrups, arabinose, ribose, maltose, lactose, cellulose, modified cellulose, maltotriose and raffinose, sugar alcohols such as sorbitol, glucitol, erythritol, lactitol, maltitol or xylitol, carboxylic acids and their salts, more particularly uronic or aldonic acids such as gluconic acid or sodium gluconate, inulin or modified inulin, pectin, dextrins and cyclodextrins, and mixtures thereof.

7. 7. A powder composition according to claim 6, wherein the composition has a t of 20 min or more, in particular 30 min or more, in particular 60 min or more, more particularly 80 min or more, even more particularly 100 min or more. ６０ A powder composition comprising:

8. 8. Powder composition according to claim 6 or 7, wherein the calcium magnesium compound is selected from the group consisting of quicklime and quick compounds having an effective CaO content of at least 40% by weight, preferably at least 50% by weight, more preferably at least 65% by weight, preferably at least 70% by weight, more preferably at least 75% by weight, advantageously at least 80% by weight and even more advantageously at least 90% by weight, based on the weight of the calcium magnesium compound.

9. The powder composition according to any one of claims 6 to 8, wherein the calcium magnesium compound has a particle diameter d ９９ is less than 2 mm, particle diameter d ５０ is greater than 3 μm, more particularly greater than 4 μm and up to 90 μm.

10. 10. The composition according to any one of claims 6 to 9, wherein the organic additive is present in an amount of at least 2% by weight, preferably at least 3% by weight, more preferably at least 4% by weight, more preferably at most 10% by weight, preferably at most 7% by weight, more preferably at most 6% by weight or 10-20% by weight, based on the weight of the calcium magnesium compound.

11. 11. The powder composition according to claim 6, wherein the calcium magnesium compound is quicklime having at least one of the following characteristics: a total content of available CaO and MgO is equal to or greater than 80% by weight; and an available lime content is at least 70%.

12. Powder composition according to any one of claims 6 to 11, wherein the calcium-magnesium compound is lime, in particular quicklime.

13. A product obtainable by the method according to any one of claims 1 to 5, having a compressive strength Rc of less than or equal to 2 MPa after 28 days, preferably at 40°C.

14. Use of the powder composition according to any one of claims 6 to 13 for treating excavated material to form a stabilized soil having an immediate support index of at least 5% and a compressive strength Rc of at most 2 MPa after 28 days (preferably at 40°C).

Images